Free machining ferrous alloy



I Patented July 30, 1935 K UNITED *STATES FREE MACHINING FERROUS ALLOYFrank R. Palmer, Reading, Pa., assignor to The Carpenter Steel Company,Reading, Pa., a corporation of New Jersey No Drawing. ApplicationJanuary 14, 1932,

Serial No. 586,697

10 Claims.

My invention relates to ferrous alloys such as are used in themanufacture of machined articles or parts; my essential purpose being toimpart relatively free machining quality to such alloys 5 by theaddition thereto of metalloid elements effective in securingsuchrelatively free machining quality; as" fully set forth in the followingspecification with clear definition of the invention in the subjoinedclaims.

In Patent No. 1,835,960 issued to me December 8, 1931, I have fully setforth the invention involved in deliberatelyusing a substantial contentof the element sulphur, to correct particularly the poor-machiningfrictional quality of corrosion resisting chromium steels. I havedetermined by extensive experimentation that the metalloids selenium andtellurium, which group with sulphur in the periodic table of elements,

' may be employed for such purpose similarly to 20 sulphur butwith-avoidance of collateral objectionable effects and greatly improvedresults.

' My work also has been directed to a wide variety of ferrous alloyssuch as are now in extensive commercial use; including those straightcarbon and alloy steels covered by the specifications of the AmericanSociety of Automotive Engineers, Inc., and published in the S. A. E.Handbook dafed 1930 to which reference is made. I have also experimentedwith many special alloy steels not comprehended by S.'A. E.specifications such as ferritic high chromium corrosion resistingsteels, austenitic alloy steels containing high percentages ofmanganese, chromium and nickel, etc. a

In connection with my invention, I have found that the element carbon,although very important in buildingup the base composition of the alloy,plays no essential part in the application of my invention-as I haveproven by experimenting with alloys containing from the lowest carbonpracticable in commercial manufacture up to the highest carbon commonlyused in tool steel analyses. The element, carbon, is therefore ignoredin the following specification and claims with the understanding that itmay be used in compounding the base analysis in accordance with thepractice well known to the art. Broadly speaking, the ferrous alloys towhich my invention relates may be divided into four general classeshaving fairly well understoodbut not definitely definable boundaries.The first class comprises the non-alloy or so-called straight carbonsteels, containing approximately 98% or more of iron, and typified inthe S. A. E. specifications under the 1000 series. This class would alsoinclude commercially pure ingot iron. In the steels of this class, thecarbon is adjusted to suit requirements, manganese is present in variousamounts up to 1.55%, phosphorous and sulphur (with exceptions) occur asunavoidable impuritiea'and possibly silicon up to about 50%, withoutdeparting from the conception of a straight carbon steel. In the S. A.E. 1000 series are found such steels as X4315 containing low carbon,1.25/1.55% manganese, .05% phosphorus, and .080/.130% sulphur.Nevertheless, such modifications are commercially regarded as non-alloysteels and for the purpose of this invention are so considered. A secondclass can be formed to comprehend the so-called structural alloy steels,commonly employed for heat treated machine parts and in which the ironbase may approximate 90%, to 98%as embraced for example, by S. A. E.series 2000, 3000, 4000, 5000, 6000 and 9000. Thus it appears that theseso-called structural alloy steels are distinguished from the straightcarbon steels by the presence of one or more of the group of metallicalloying elements comprising manganese, chromium, nickel, vanadium, andmolybdenum. Obviously these structural alloy steels can be compoundedoutside of the specific limits set by the S. A. El specification, butsuch steels, some of which contain other alloys such as tungsten wouldbe readily classified by those familiar with the art as belonging to thestructural alloy group which I have defined. The third class wouldcomprehend the higher carbon and harder -materials-usually employed forthe manufacture of tools and which ordinarily can be hardened harderthan about on the C scale of the Rockwell hardness testing. This wouldembrace such steels as S. A. E. 1095, 52100, 6195, the 7000 series, anda wide ,variety of other hardenable alloy steels readily recognized bythe trade as tool" steels. The alloy content of the "tool steel classvaries widely from less than 1% up to about- 30% as in the cobalthigh-speed steels; the'balance being iron. The fourth class is really aremainder containing "special alloy steels not embraced by the threeclasses already mentioned;

including high chromium ferrous alloys of the corrosion resisting type;austenitic alloys of the high manganese, high nickel or nickel-chromiumtype; high silicon alloys used for electrical purposes; tungsten orcobalt magnet steels, etc.; in which the percentage of iron may run aslow as 50% of the total, the balance comprising alloying elements. Inthe prosecution of my invention I have experimented with a variety offerrous alloys in each of the above four broad classes giving particularattention to the ferritic highchromium, corrosion-resisting alloys andthe austenitic ferrous alloys; 'all' as hereinafter described.

Since this invention has for its object the production of ferrous alloysof relatively freemachining properties, some apparent facts regardingthe machinability of ferrous alloys in general should be considered.Diflicult machining of ferrous alloys arises from a number ofindependent causes but these causes are frequently combined in a givenalloy. Some alloys are diflicult to machine because of their inherenthardness, as for example high speed tool steel,

more diflicult to cut. Somewhat related, butstill different from thelast mentioned cause for difficult machining, is. the inherent toughnessof the alloy being cut. Two steels of the same hardness and the sameultimate tensile strength may machine very differently due to the factthat one is comparatively brittle while the other is comparativelytough; the tough steel being the more difficult because it requires morework to tear off the chips. This same difliculty of toughness seriouslyinterferes with machining some ferrous alloys after they have beenannealed too soft, when they exhibit a stringy tendency with likelihoodof tearing, and the chips are most diflicult to clear. from the tools.In such cases, it is well known that machinability can be im-. proved bynot annealing them too soft, in. which case they will machine bettereven though they are harder and have a higher tensile strength. Stillanother source of variable machining quality is to be found in thestructural composition of the alloy. This is well illustrated in thecase of straight carbon tool steel which may be annealed in such amanner as to produce a predominanceof lamellar pearlite on the onehandor a predominance of spheroidized cementite on the other. Although theanalysis and hardness may be the same in each case, a great differencewill be found in machinability, usually favoring the spheroidized steel.Difficult machining properties are introduced in some steels-'- notablythe high chromium, corrosion resisting steels-by reason of highfrictional properties which tend to cause the chips to adhere to thecutting edge-of the tool and produce what is commonly known as a bug.This seriously interferes with the speed of cutting and the smoothnessof the cut and is generally recognized as acause independent of allother machining difficulties.

For many years, it has been generally known that a comparatively highsulphur content will render a steel more free-machining. Of course,

. limit, the S. A. E. specifications hardly tolerating it in percentagesover .05 and it being usually required to be much lower; an exceptionbeing found however in so-called screw stock where sulphur ispermissibly used in percentages up to .15 in order to obtain. speciallydesired free-machining quality.

While a relatively large sulphur content may be deliberately andeffectively employed for securingmachinability in screw stock and as setforth in my Patent No. 1,835,960 above referred to, I have found thatthe collateral objectionable defects incident to use of this elementpractically limit its satisfactory commercial employment; the factappearing that sulphur combines with a metal present in the alloy toform a sulphide which occurs as a slag-like inclusion hardly soluble inthe ferrous matrix. While these slaglike sulphides occur usually in moreor less globular form in the cast ingot, in forged or rolled productsthey are drawn out into long stringers which impair the quality of themetal and particularly depreciate its transverse ;ductility. Thisapparent fact supports the great prejudice against a sulphur content incommercial alloys, so as to interfere in any case with its generaluse inthe manufacture of free-machining alloy steels, notwithstanding thegreat desire on the part of industry to secure metals which can befreely, rapidly and economically cut.

I have discovered that metalloid of the group selenium-tellurium can beadvantageously used in a great number of ferrous alloys, to securefree-machining properties comparable to those which could be secured bythe use of sulphur but with scarcely any of the disadvantages ofsulphur. I have also discovered that certain very tough ferrous alloys,such as those of the austenitic group, can be further improved and mademore free-machining by the addition of an embrittling element such asphosphorus or arsenic in conjunction with the selenium or telluriumaddition. My experiments show that the invention operates satisfactorilyon castings as well as on rolled or forged alloys.

Selenium and tellurium, in all steels that I have investigated, differprimarily from sulphur in the fact that they are largely soluble in theferrous matrix, onlya small residuum being present in the form ofslag-like inclusions. It is quite evielements and, furthermore, in manycases they seem more potent in their benefits than sulphur, since asmaller total percentage of them is necessary in order to producesatisfactory machining qualities.

In that non-alloy or straight carbon steel group previously referred to,I have variously added selenium 'and tellurium and find that it can beeffectively used to replace the sulphur of common screw stock with onlya. small percentage of resulting slag-like inclusions. Such steels arefreely machinable but are much stronger, tougher and more commerciallyusable than the high sulphur product known as screw stock. I havefurther experimented with selenium and tellurium in steels containingmanganese, similar to S. A. E. X 1315, and also with lower manganese,such as S. A. E. 1112, but find that I always get freemachiningqualitywith a minimum of slag-like inclusion and no evidence ofred-shortness, which would indicate that abnormal manganese is in no waynecessary to compensate for the presence of selenium and tellurium.

. through my invention, are now made available to In the grouppreviously referred to as structural alloy steels, I have experimentedwith' nickel steels, nickel chromium steels, nickel molybdenum, chromemolybdenum, straight chromium, chrome vanadium, silico-manganese steels,and others and find, regardless of thebase alloy composition of thematerial, that selenium or tellurium, or the two metalloids jointly,

produce relatively free-machining qualities with.

a minimum of slag like inclusions and with verymuch less detriment inany case, to the high quality of the alloy, than, wouldbe incurred byusing an equivalent percentage of sulphur for such purpose.

For example, I have taken the base analysis represented by S. A. E 3250and have added selenium and/or tellurium in percentages ranging fromabout .05% to about 2%. I. have com pared these selenium-telluriumalloys with a similar composition without seleniumor tellurium and findthat the tensile strength, the response to heat treatment, the ductilityand the impact resistance are not aiIected to any objectionable extent.It is indicated by experiments on this and other base compositionsfalling within the structural alloy group that these steels,

machining qualities inevitably follow the addition of appropriatequantities of selenium o'r tel-i lurium, or both. Apparently the use ofthese metalloidsdoes not seriously interfere with the hardeningproperties of these tool steels nor. wit their utility in the formoftreated tools. I

I have also investigated the effect of selenium, tellurium, phosphorusand arsenic on various ferrous alloys within the special alloy class.

As is well known, some commercial alloys within this class are very hardor very brittleor both-and will scarcely lend themselves under anycircumstances to free-machining. For

example I have studied the high silicon steels used forelectrical'purposes and find that an ironsilicon alloy containingapproximately 6% silicon is very brittle ,(having negligible elongationin a tensile test) and hard (over 250 Brinell hardness). When attemptingto cut a thread on such alloyswith a threading die, the alloy simplycrumbles under the tool and is destroyed. It is therefore obvious thatin this special alloy classmy selenium-telluriuminvention can only beapplied to ,base alloy compositions that have commercial machiningpossibilities, that is practically to alloys capable of being annealedto softer than 15000 pounds tensile strength per square inch.

I have studiedfin considerable detail the eifect' of selenium andtellurium on that class of ferritic high chromium, corrosion resistingsteels and irons containing chromium from 4% to 60% and find thatseleniumor tellurium, or both used Jointly, are even more effective thansulphur as described in my Patent No. 1,835,960 in producingfree-machining qualities. The seleniumtellurium addition appears to actequally as well as'sulphur in reducing the high frictional qualitycontaining from about 15%: to 50% nickel, and I the high chrome-nickelalloys containing a total chromeenickel content from about 20% to 50%,the principal part of the balance in all cases being iron. In this groupof alloys I find that the useof selenium and/or tellurium in quantityfrom .03% to 2.00% effects a noticeable improvement in machinability butbecause of the super tough nature of these alloys they cannot be cut asrapidly as is commercially desired. Austenitic ferrous alloys, whensubjected to a tensile test commonly show an elongation in 2" or 40% ormore .with corresponding high impact tough ness. .1 have found that thisexcessive toughness can well be. reduced by adding in addition to theselenium or tellurium, an embrittling agent such as phosphorus therebyreducing the elongation in 2" by 10% or even 20%, greatly improving thefree cutting qualities of the alloy. and yetnot reducing theeffectivetoughness of the alloy sufiiciently to interfere with its applicationfor bolts, nuts, pump shafts, valve parts etc.. where free machiningqualities are highly desirable; Also these austenitic ferrous alloysretain their characteristically lower magnetic qualit es when treatedwith selenium or tellurium and phosphorus as described. 'The amount ofembrittling agent to be used may vary from .05% to 50% depending on thedegree of brittleness desired, about .12% to .18% being sufiicient inconjunction with selenium or tellurium to reduce the elongation by about10% and is ample for most purposes. The use of an embrittling agentalone. without selenium or tellurium, has very little beneficial efiecton the machinability of an austenitic alloy and my inventioncontemplates that the embrittling agent shall always be actheseexplanations seem to adequately explain the behavior of selenium andtellurium, since there is a minimum of slag-like inclusion, very littlediscontinuity in the metallic matrix and very little evidence ofdecreased toughness as a result of that portion of the selenium and tellurium which dissolved in the ferrous matrix.

I find apparent benefit in using the selenium and tellurium elementsjointly, inasmuch as each element is largely soluble but partlyinsoluble in the ferrous matrix. It would appear that greater quantitiesof these metalloids can be used jointly to produce a smaller quantity ofslag-like inclusions than results if either of the metalloids is usedsingly in the same amount. I have also observed that sulphur may besupplemented by the use of selenium or tellurium, or both, in or der toproduce better machining qualities, but. ordinarily I prefer to keep thesulphur low be-- cause of the insolubility of its metal-sulphides.

I find noparticular advantage or disadvantage to the use of so-calledneutralizers such. as manganese, zirconium, etc.; in connection .with myselenium-tellurium addition. These neutralizers do not appear necessaryin order to insure hotusing the selenium or tellurium therewith.

Selenium and tellurium are commercially available in the elemental formand Ihave seen them most generally in the formof a powder. This powderdoes not lend itself readily to making additions to the molten alloy andI therefore find it advantageous to first produce an alloy of iron andselenium or iron and tellurium and then add this alloy to my moltenbath. Both selenium and tellurium, when mixed with finely divided ironand heated to a black-red temperature, will combine with evolution ofheat to form a product which is suitable for steel making addition's ofiron and 50% of the metalloid appearing to make a satisfactorycombination-although it is entirely likely that their admixture in someatomic proportions would produce a more stab compound.

In making my free-machining alloy, I melt in the open hearth, electricfurnace, crucible furnace, or by other means, the base ferrouscomposition and then add my iron-tellurium or iron-selenium alloy at theend of the melt in a manner which seems best calculated to give maximumyield of the added metalloid. For example, in the high frequency,electric induction furnace, I add my iron-selenium or iron-telluriumalloy a few minutes before the heat is ready for, pouring and it isveryrapidly assimilated by the bath. I find that small-additions up to about110% incur scarcely any loss of metalloid and even with additions up to20%, the percentage lost is small. As the percentage of metalloid .addedincreases, the amount lost through volatilization also increases so thatto get percentages as high as 2%, it is presently indicated that atleast twice this amount mustbe added. This loss, however, can doubtlessbe further reduced by more expert manipulation and the employmentof-means which are commonly known to the steel making art. In the caseof open hearth or arc electric furnace steel, the addition 'can well bemade to the ladle, throwing the iron-selenium or iron-tellurium compoundinto the flowing stream.

'I have observed that the addition of tellurium to a molten steel bathhas rather dangerous toxic effects; such molten tellurium alloys givingoff voluminous fumes very disagreeable and dangerous to the workmen.This difficulty has limited my work on tellurium steels to a point onlysufficient to establish the facts herein stated that either selenium ortellurium or both Jointly may be employed for the purpose of myinvention. Their absolute quantitative equivalence is not to beunderstood, and in the case of some "special alloy steels I haveoccasionally observed that tellurium seems more effective than seleniumin producing free machining qualities and thereforemay be employed insomewhat smaller percentages for my.purposes apart from possibledifferent effects.

I have thus investigated a wide range of ferrous alloys with regard tothe effect of adding metalloid of the group selenium-tellurium, in orderto produce free-machining qualities, and find that percentages of thesemetalloids, even as small as 03% are reflected in noticeably improvedmachining qualities; these qualities be ing further improved byadditions within the range of 20% to 30% where the results aresatisfactory for most commercial purposes. I have added furtherquantities of these metalloids up to approximately 2% and find that,while these higher percentages yield improved machining alloy to anotherand from one application to another. Also the use of an embrittlingagent like phosphorus must be done with discrimination and proper regardto the purpose for which the alloy is to be used.

Essentially, my invention consists in adding to a ferrous alloy, between.03% and 2% of metalloid of the group selenium-tellurium, as required todesiredly improve its free-machining qualities with further addition ofan embrittling element when and if desired. It will be understood thatthe iron element of the alloys in all cases exceeds fifty per cent asstated, and may exceed ninety eight per cent as in straight carbonsteels and commercially pure ingot iron; and that various substantialpercentages of different me- In the subjoined claims the term balanceisubstantially iron contemplates that the balance of the composition islargely iron but may contain percentages of non-ferrous alloyingelements of such nature and in such quantity as to not alter the basicnature of the alloy for purposes'of my invention. For example, in myspecial alloy group there occurs a steel having the following nominalcomposition:

o .10% or. 18.00% Ni. 8.00%

Many modifications of this basic composition are well known to the artcontaining added percentages of other alloying elements:

C .10% Cr 18.00% Ni 8.00% Ti 1/2.0% .10% C1 18.00% Ni 8.00% Cu 2.45%.10% Cr 18.00% Ni 8.00% W 3.80% .10% Cr 18.00% Ni 8.00% Me 3.42% .10% C118.00% Ni 8.00% Si 4.59% (I .10% Cr 18.00% Ni 8.00% Al 2.00%

What I claim is: 1. A ferrous alloy for the manufacture of machinedarticles containing: .03 to 2.00% metalloid of the groupselenium-tellurium and .05% to 50% C C C C of an embrittling agent ofthe group phosphorusmium between 4% and 45% and nickel between and 46%with a total percentage of said elements between and 50%, metalloid ofthe group selenium-tellurium .03% to 2.0% phosphorus .05% to 50%, thebalance being substantially iron and the alloy being characterized byrelatively free machining properties.

3. The combination of from .03% to 2% metalloid of the groupselenium-tellurium with an inherently machinable ferrous base, thelatter comprising allowing elements and from 50% to 98% of iron andbeing capable of annealing softer than 250 Brinell hardness. and thecombination of said metalloid with said base imparting materiallyincreased machinability to the resulting alloy.

4. The combination of from .03% to 2% metalloid of the groupselenium-tellurium with an inherently machinable ferrous base, thelatter comprising alloying elements and from 50% to 98% of iron andbeing capable of annealing softer than 150,000 pounds per square inchultimate tensile strength with more than 3% elongation stantially iron;the resulting alloy being characterized by relatively free machiningproperties.

6. An austenitic alloy characterized by relatively free-machiningproperties. containing 5% to 50% of metallic alloy of the groupmanganesenickel-chromium, .03% to 2% of metalloid of the groupselenium-tellurium, .05% to .50% of phosphorus, and the balancesubstantially iron.

7. The combination of from .03% to 2% metalloid of the groupselenium-tellurium and .05% to .50% phosphorous with an inherentlymachinable ferrous base, the latter comprising alloying elements andfrom 50% to 98% of iron and being capable of annealing softer than 250Brinell hardness; the combination of said phosphorous and metalloid withsaid base imparting materially increased machinability to the resultingalloy.

8. The combination of from .03% to 2% metalloid of the groupselenium-tellurium and .05%

to .50% phosphorous with an inherently machinable ferrous base, thelatter comprising alloying elements and from 50% to 98% of iron andbeing capable of annealing softer than 150,000 pounds per square inchultimate tensile strength with more than 3% elongation in two inches andthe combination of said phosphorous and metalloid with said baseimparting materially increased machinability to the resulting alloy.

9. An alloy containing essentially chromium between 4% and 45% andnickel between 5% and 46% with a total percentage of said elementsbetween 10% and 50%, metalloid of the group selenium-tellurium .03% to2%, the balance being substantially iron and the alloy beingcharacterized by relatively free machining properties.

10. An austenitic alloy steel containing essentially chromium between 4%and 35% and nickel between 5% and 46% with a total percentage of saidelements between 10% and 50%, .03% to .2% tellurium, the balance of thesteel being substantially all iron and the alloy steel beingcharacterlzed by relatively free machining properties.

FRANK R.

CERTIFICATE OF CORRECTION.

Patent No. 2,009,713. July 30, 1935.

FRANK R. PALMER.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 3,first column, line 65, for "15000" read 150000; and second column, line21, for "or" first occurrence, read of; page 4, second column, afterline 70, insert the following paragraph: Such modified types are stillin need of improved machinability and these added percentages of copper,.tungsten, molybdenum, etc., while substantial, do not obscure the basicnature of the austenitic chrome-nickel analysis. or interfere with theapplicability of my invention. Therefore, such extra alloys arecomprehended in my term "balance substantially iron".; page 5, firstcolumn, line 7, claim 2, after "2.0%" insert a comma; and line 14, claim3, for "allowing" read alloying; and that the said Letters Patent shouldbe read with these corrections therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 10th day of September, A. D. 1935.

Lea-l ie Frazer (Seal) Acting Commissioner of Patents.

